The invention is in the field of tape feeders, particularly feeders for stepwise indexing of tapes having pockets containing surface mountable electrical components.
Typically, a tape is advanced stepwise to sequentially present each pocket to a pick-up station where the component is removed from the pocket for subsequent handling, such as transfer to a conveyor or direct placement onto a circuit board. Typically, a top cover of the tape is peeled sufficiently from the substrate so as to open each pocket in turn, and thus provide access to the component therein. Auxiliary covers or movable "shutters" often are provided to prevent loss of components from opened pockets.
Several types of supply tapes are used presently, and the apparatus of the invention is applicable to them. One type has a plastic substrate embossed to define component holding pockets which are enclosed by a separable thin plastic top cover; and the other type has holes all the way through a cardboard substrate with top and bottom covers for the holes so as to define the component pockets.
The prior art cross-referenced above generally discloses peeling of the tape cover by indexing a take-up reel along with indexing of the component supply tape. The cover is passed around a fixed guide surface and maintained under tension by the take-up reel.
A particular problem encountered by the industry in use of these tape feeders is breakage of the cover tape and the resultant loss of components and "down time" of the apparatus. Typically, the take-up reel acts to maintain a tension on the cover material at all times, so that the tension varies as more of the cover material is wound onto the take-up reel. Thus, angular displacement of the take-up reel must be sufficient to provide the necessary tension for peeling of the cover material from the supply tape even when the take-up reel is substantially empty. Since the amount of rotation of the take-up reel is the same for each indexing step, the peeling tension imparted to the cover tape increases as the take-up reel becomes more full.
Typically, the cover material is attached to the substrate of the supply tape by a heat seal between each individual pocket of the supply tape and along the edges thereof. The force necessary to peel the cover material from the substrate can differ from tape to tape because of such factors as pressure on the heat sealing rolls, widths of the tapes, and spacing of the pockets. Thus, the tension imparted to the cover material of one tape by a substantially empty take-up reel may not be sufficient to peel the cover from another tape.
Variations in peeling tension by the changing diameter of the reeled cover material, and variations in strength of connection of the cover material to the substrate, typically are accommodated by ensuring that the "initial peeling tension" imparted to the cover material by a substantially empty reel is sufficiently large to overcome the strongest bond between cover and substrate. In turn, cover materials which require less peeling force more frequently break as more cover material is wound onto a take-up reel which provides a peeling force sufficient to overcome the stronger bonds of other tapes.
Cover material breakage requires human intervention to splice or rethread the cover material to the take-up reel which, in turn, may require the stripping of the cover material from as much as one-hundred of the pockets in order to provide enough of a "leader" of cover material for reconnection to the take-up reel. The number of components lost from pockets when covering material is stripped to provide the "leader", and the down-time involved in performing the splicing or rethreading, are costs that it is desirous of eliminating or minimizing. Further, loss of time can become compounded when the feeders are "bricked" together side-by-side to provide the maximum amount of feeders in a minimum amount of space and is a particular problem when a pick-up spindle which can't detect the presence or absence of a component (a so-called "dumb" spindle) is used to remove the components from the pockets.
It has also been found that the peeling force required for supply tapes that are stored at temperatures greater than room temperature often increases.
The instant invention provides for minimization of the peeling tension. In a preferred embodiment of the invention, the supply tape and cover material are indexed forward before the peeling tension is applied, so that the actions of feeding and peeling are performed separately. It has been found that this separation of steps requires a lesser (usually constant) peeling tension on the cover material in order to peel it from the substrate than prior art peeling methods and apparatus.
It has also been found that retraction of the guide surface, around which the cover tape is passed during peeling, reduces the tension necessary to accomplish the peeling. It has also been found to be beneficial for this retraction of the guide surface to be caused by the cover material and the tension applied thereto during the peeling step.
Additionally, the instant invention provides for relief (or at least reduction of) the tension on the cover material during feeding of the supply tape prior to the peeling step.
It is also contemplated that peeling can occur during feeding of the supply tape wherein the peeling guide surface is retractable during such feeding to lessen the tension necessary to accomplish peeling of the cover from the substrate. For instance, the guide surface may be spring biased toward the feeding direction of the supply tape so as to move in that direction when tension is removed from the cover between feeding steps.